Continuous tone ZnO - acrylic polymer binder and additive

ABSTRACT

Electrophotographic continuous tone reproduction sheet in which the coating composition therefor includes continuous tone zinc oxide pigments, an insulating polymer resin binder selected to provide uniform optical density of the finished product, and in addition preferably includes an additive to enhance the optical density properties of the finished product.

United States Patent Perlis et al.

[ Dec. 30, 1975 CONTINUOUS TONE ZNO ACRYLIC POLYMER BINDER AND ADDITIVEInventors: Barry R. Perlis, Lexington; Michael E. Nelson, Worcester,both of Mass.

Dennison Manufacturing Company, Framingham, Mass.

Filed: Aug. 5, 1974 Appl. No.: 494,492

Related U.S. Application Data Continuation of Ser. No. 63,933, Aug. 14,1970, abandoned.

Assignee:

U.S. Cl. 96/l.8; 96/1.5; 96/l.7 Int. Cl. 603G 5/08 Field of Search96/15, 1.7, 1.8

[56] References Cited UNITED STATES PATENTS 3,347,670 10/1967 Nelson eta1 96/15 Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, orFirm-George E. Kersey [57] ABSTRACT 8 Claims, No Drawings CONTINUOUSTONE ZNO ACRYLIC POLYMER BINDER AND ADDITIVE This is a continuation ofapplication Ser. No. 63,933, filed on Aug. 14, 1970, now abandoned.

FIELD OF INVENTION The present invention relates to electrophotographicreproduction sheets and/or to electrophotographic coating compositionsand more particularly to sheets and coating compositions capable ofproducing continuous tone prints of photographic quality from anoriginal.

BACKGROUND OF THE INVENTION Conventional silver halide technology is themethod most used today for reproducing and enlarging pictures andtransparencies. Although usual photographic techniques produce goodquality prints of originals, the expense involved and the time requiredto produce a copy are major disadvantages.

Over the years attempts have been made at utilizing electrophotographic,electrostatic or electrofax techniques to reproduce pictures andtransparencies. Although somewhat satisfactory results have beenobtained, systems utilizing such techniques have not become widelyutilized primarily because the quality of the reproduction was notgenerally as high as could be achieved using standard photographicreproduction procedures. I

Generally these systems suffered from prints that lacked uniform opticaldensity, i.e. smoothness and fill-in across a predetermined area, ineach step of the usual gray scale. Thus, in prints produced by thesetechniques, large variations in grayness would appear in an area whichshould have been one continuous tone.

In addition, the prints of the prior art were usually limited to four toseven steps or graduations on a 21 step photographic gray scale of 0. l5 (O.D.) increments optical density. For photographic quality prints, ithas been found that about 15 or more steps are necessary to provideprints which are competitive with those produced using silver halidephotoreproduction chemicals and techniques.

THE INVENTION REDUCES THE PRIOR ART DISADVANTAGES The present inventionprovides an electrophotographic sheet and coating composition which canprovide prints having about 15 or more steps (latitude) on a 21 stepgray scale and a very small drop-off variation in optical density andtherefore good smoothness and fill-in across a predetermined area.

BRIEF DESCRIPTION OF THE INVENTION In order to provide the improvedelectrophotographic sheet as well as the coating therefor suitable foruse in continuous tone electrophotograhic applications, a coating isformed which contains what is known in the trade as continuous tone zincoxide pigments.

Continuous tone electrophotograhic zinc oxide pigments are generallywhite, readily accept dye sensitizers and are particularly useful toreproduce various tones or shades of gray. This type of zinc oxidepigments can, for example, be purchased from the New Jersey ZincCompany, of New York, N.Y., as either grade CT-Ol 1 of CT-l2.

The coating also contains as insulating binder for the pigments. Incontinuous tone applications it has been found that the insulatingbinder composition utilized in the coating should have electricalproperties which will provide good optical density as well as a broadlatitude (number of distinct degrees or steps of grayness).

Various resin systems have been tested, but to date the best and mostpreferred binder resins uncovered are the acrylic polymer resins havingproperties suitable for electrophotographic applications. The mostoutstanding acrylic polymer binders uncovered to date are thestyrene-acrylate resins and more particularly such polymers havingrepeating styrene and ethyl acrylate as units. A polymer of this classmay be purchased from Desoto, Inc. of Des Planes, Illinois, U.S.A. underthe designation Deso'to E-048. In addition to the above, it has beenfound that the alkyd resins suitable for electrophotographicapplications may also be utilized as the binder, but these are lesspreferred since they give somewhat poorer density, latitude andsmoothness of print. An alkyd resin suitable for such purposes may beobtained from the aforementioned Desoto, Inc. as Desota E09. It has alsobeen found that a combination or mixture of both alkyd and acrylicpolymer resins may be utilized although again not providing propertiesequal to the acrylic polymer resin itself. Such resins as, for example,the Desoto resins E09 and E048 may be combined in a 1:1 ratio or may becombined in any other ratio as, for example, 1:10 or 10 to 1.

The aforementioned resin, including the Desoto resins, are generallysold as a solution e.g., in toluene having about 50% solids by weight,although obviously the percentage solids can vary;

It has been found in practice for continuous tone electrophotographicapplications the pigment to binder solid ratio by weight should bebetween 9 to 1 and 3 to 1, between 7 to l and 4 to 1 being preferred,and a ratio of 5 parts pigment to 1 part binder resin solids by weightbeing most preferred. It has been found in practice that when the ratioexceeds about 9 to 1, adhesion of the coating to the base paper of thesheet substantially decreases and in addition, the uniform opticaldensity of the end product (print) substantially deteriorates. At ratiosless than 3 to 1, it has been found that blotchiness and non smoothnessbegins to appear in the resulting product (print) to a degree where goodquality reproduction is no longer achievable. It has also been foundthat for continuous tone applications the binder and pigments, whenformed into a coating, should have a saturation voltage between 300 tovolts and most preferably between about 250 to volts. It has also beenfound to provide optimum continuous tone reproduction that the coatingshould exhibit substantially a linear charge voltage decay in thepresence of light. Coatings used in normal electrophotography generallyexhibit a non-linear decay. Substantially linear light decay has beenaccomplished in this invention by using the aforementioned coatingformulations.

The coating herein is mixedand processed using conventional techniquesand is then applied to a electrophotographic base paper such asWeyerhauser Paper Company, sold under the designation of CC Base. K.

It has been found in practice that for continuous tone applications thepaper should preferably weigh about 35 to 90 lbs/3000 square feet ream,and preferably be about 2 to 4 mils thick, but it should be understoodthat 3 this is not critical and can vary over a wide range dependingupon the applications.

In continuous tone applications, it has been found that the coatingweight (binder pigment) should preferably be between 12 to 25 lbs. per3000 square feet of paper and most preferably between 14 to 20 lbs. per3000 square feet of paper.

In addition, it is preferable that the coating have a thickness of 0.4to 0.8 mils, and most preferably a thickness of 0.5 to 0.7 mils.

As another important feature of this invention, it has been found inpractice that the optical properties, in particular the uniform opticaldensity of the finished print is enhanced by the use of a polymer(resin) additive. The preferred class of polymer resin additives havethe repeating unit where R is lower alkyl or hydrogen, R is lower alkylor hydrogen and where the above lower alkyl has 1 to 4 carbon atoms(i.e. methyl, ethyl, propyl, butyl). Most preferably R or R is methyland most preferably one is methyl while the other is hydrogen.

in practice it has been found that the polymer resin poly-a-methylstyrene, such as sold by Dow of Midland, Michigan, provides the bestresults as a resin additive although poly-vinyl toluene resins, that iswhere R is ortho, meta, or para methyl and R is hydrogen, may also beused. For continuous tone electrophotographic applications it has beenfound that additive should be employed such that the amount thereof isto 40% by weight of the solid binderfMore preferably the amount ofadditive should be to 30% of the weight of the binder solids and mostpreferably 10 to of the weight of the binder solids.

As in most conventional electrophotographic coatings, the coatingpreferably includes sensitizing dyes to achieve wider spectral response.Various sensitizers well known in the art may be used, as for example,those disclosed in U.S. Pat. No. 3,469,979, as well as those disclosedin the Examples herein.

After the sheet is formed it is utilized in a conventionalelectrophotographic copier, such as that sold by Dennison ManufacturingCompany, Framingham, Mass. as the Dennison Standard Copier, except thatthe machine is modified so that the sheet is permitted to undergosaturation or near saturation development.

This is accomplished by slowing the movement of the sheet through thetoner used to develop the sheet. It has been found that this can beaccomplished by permitting an immersion time in the toner to 15 secondsalthough this can vary depending on the toner and concentration thereofused. Well known toners which are usable include those manufactured byHunt Chemical Corp., lnterchemical, and Bell and Howell, among others.

In use the electrophotographic sheet of this invention is passed throughthe copier such that it is first charged using corona charging until itreaches maximum charge acceptance, generally 1 to 2 seconds beingsufficient, is then exposed to light and then is permitted to undergosaturation or near saturation development. Thereafter, the print isdryed in a conventional manner. Photoreproduction sheets made inaccordance with this invention were used in the Dennison Standard Copieras modified above and prints of photographs were made and were of goodquality approximately that of the original in tone and latitude.

DETAILED DESCRIPTION EXAMPLE 1 Mix 20 gms. of Desoto E 048 (which is amixture of 50% solids in toluene) styrene ethyl acrylate resin binderwith 45 gms. of toluene solvent. Then mix into it 3 gms. of Dow 276-V2poly alpha methyl styrene. Add 50 gms. of New Jersey Zinc ContinuousTone ZnO CT-012 together with 0.75 ml of sensitizing dye solution(prepared by mixing 0.029 grams bromophenol blue, 0.59 grams uramine(USP), 0.135 grams methylene blue dissolved in 99 grams methanol) intothe solution. After a homogeneous solution is obtained by vigorousstirring it is passed through a colloid mill in order to get a moreuniform mix and to break down the particulate agglomerates. A l-legmangauge reading of about 5 is preferably obtained.

The mix is then placed on a sheet of electrofax base paper 2 mls thick,weight 40 lbs/3000 sq. ft. and a draw down using a wire wound Mayer rodis made. The sheet is coated with the composition such that the coatingis 0.6 mls thick. The coated sheet is then dried in an oven at ll0F for2 minutes to drive out excess solvent and then the sample is preferablyplaced in a dark black bag for dark conditioning for several hours. Thesample is now ready to be used.

EXAMPLES 2 10 Using the method of Example 1, the following coatingcompositions were prepared and then applied to the base paper.

Dye Solution Toluene Dow Desoto ZnO (Formulation as Example Solvent276-V2 EO-48 (CT-012) Example 1) 2 45 gm. 20 gm. 50 gm. .75 ml 3 45 gm..5 gm. 20 gm. 50 gm. .75 ml 4 45 gm. 1 gm. 20 gm. 50 gm. .75 ml 5 45 gm.5 gm. 20 gm. 50 gm. .75 ml 6 45 gm. 1 gm. 20 gm. 50 gm. .75 ml 7 47 gm.1 gm. 25 gm. 50 gm. 1.0 ml 8 50 gm. 1 gm. 33.4 gm. 50 gm. l.25 ml 9 40gm. 1 gm. 14 gm. 50 gm. .25 ml 10 45 gm. 1 gm. 11.2 gm. 50 gm. .25 mlEXAMPLES 11 20 EXAMPLES 21 40 Using the method of Examples l-20,modified compositions of those set forth in Examples 1-20 are preparedusing the same amount and proportions of ingredients except that the dyeused was a Rose Bengal 0.5 grams and Bromophenol Blue 0.5 grams in 99grams of Methyl Cellusolve.

EXAMPLE 41 .Using the method of Example 1, a coating composition isprepared by mixing the following ingredients; toluene 45 gm., Dow G257 3gm., Desoto E-09 alkyd resin 1 1.5 gm., New Jersey Zinc Oxide CT-102 50gm.

EXAMPLE 42 Example 41 is repeated except that 0.75 ml of the dye ofExample 1 is added thereto.

EXAMPLE 43 Using the method of Example 1, a modified coating compositionis prepared by using 20 grams of a 1:1

blend of Desoto resin E048 and E09.

The above description and examples are for illustrative purposes onlyand it is not intended that the invention be limited thereto, but onlyto the products claimed in the claims appendant hereto.

We claim:

1. An electrophotographic reproduction sheet having anelectrophotographic coating consisting essentially of continuous tonezinc oxide pigment providing about 15 or more steps on a 2l-stepphotographic gray scale of 0.15 (O.D.) increments, an insulating acrylicpolymer binder therefor and a polymer resin additive having therepeating unit where R is lower alkyl or hydrogen,

R is lower alkyl or hydrogen, and

wherein said lower alkyl has 1 to 4 carbon atoms,

positioned on a base paper, said pigment and binder having a ratio byweight in the range from about 9:1 to about 3:1, and said additive beingpresent in an amount which is in the range from about 5 to 40 percent ofsaid polymer binder.

2. A sheet according to claim 1 where R is CH and R is hydrogen.

3. A sheet according to claim 1 where R is hydrogen and R is Cl-I at theortho, meta or para position of the phenyl ring.

4. A sheet according to claim 1 in which the resin additive is 10 to 30%by weight of the polymer binder solids.

5. A sheet according to claim 1 in which the polymer binder is astyrene-acrylate resin.

6. A sheet according to claim 1 in which the polymer binder is astyrene'ethyl acrylate resin.

7. An electrophotographic sheet according to claim 1 in which the basepaper has a weight of 35 to lbs. per 3000 sq. ft. reamand wherein thecoating is applied at a weight between 12 to 25 lbs. per 3000 sq. ft.ream.

8. An electrophotographic sheet according to claim 1 in which thecoating contains a sensitizing dye.

1. AN ELECTROPHOTOGRAPHIC REPRODUCTION SHEET HAVING ANELECTROPHOTOGRAPHIC COATING CONSISTING ESSENTIALLY OF CONTINUOUS TONEZINC OXIDE PIGMENT PROVIDING ABOUT 15 OR MORE STEPS ON A 21-STEPPHOTOGRAPHIC GRAY SCALE OF 0.15 (O.D.) INCREMENTS, AN INSULATING ACRYLICPOLYMER BINDER THEREFOR AND A POLYMER RESIN ADDITIVE HAVING THEREPEATING UNIT
 2. A sheet according to claim 1 where R1 is CH3 and R2 ishydrogen.
 3. A sheet according to claim 1 where R1 is hydrogen and R2 isCH3 at the ortho, meta or para position of the phenyl ring.
 4. A sheetaccording to claim 1 in which the resin additIve is 10 to 30% by weightof the polymer binder solids.
 5. A sheet according to claim 1 in whichthe polymer binder is a styrene-acrylate resin.
 6. A sheet according toclaim 1 in which the polymer binder is a styrene ethyl acrylate resin.7. An electrophotographic sheet according to claim 1 in which the basepaper has a weight of 35 to 90 lbs. per 3000 sq. ft. ream and whereinthe coating is applied at a weight between 12 to 25 lbs. per 3000 sq.ft. ream.
 8. An electrophotographic sheet according to claim 1 in whichthe coating contains a sensitizing dye.